She gave Jenny McCarthy a platform to promote the discredited idea that vaccines cause autism.

Former daytime television superstar and rumored Democratic presidential candidate Oprah Winfrey won the Cecil B. DeMille Award at Sunday night’s Golden Globes. In the “complicated times” we live in, she said during her acceptance speech, “speaking your truth is the most powerful tool we all have.”

While such bromides may play well with an audience of entertainers, Ms. Winfrey’s applause lines should be a warning to those who take her political ambitions seriously. She built her media empire by crafting pleasing narratives....

Former daytime television superstar and rumored Democratic presidential candidate
Oprah Winfrey
won the Cecil B. DeMille Award at Sunday night’s Golden Globes. In the “complicated times” we live in, she said during her acceptance speech, “speaking your truth is the most powerful tool we all have.”

While such bromides may play well with an audience of entertainers, Ms. Winfrey’s applause lines should be a warning to those who take her political ambitions seriously. She built her media empire by crafting pleasing narratives. She isn’t interested in boring things like data and facts. She has difficulty acknowledging that some things are true and some things are not.

Like President Trump, who for years made inflammatory remarks about vaccines and even flirted with the idea of appointing noted skeptic
Robert F. Kennedy Jr.
to a vaccine safety commission, Ms. Winfrey has a penchant for promoting the myth that vaccines are dangerous. While she claims publicly to be pro-vaccine, she has allowed antivaccine megastars a platform to share “their truths.” Yet those “truths” aren’t true at all. They are a collection of unsubstantiated and conspiratorial charges linking vaccines to autism—never mind the mountain of evidence to the contrary.

Ms. Winfrey’s biggest gift to the antivaccine movement came in September 2007 when she invited the actress
Jenny McCarthy
to appear on her top-rated talk show. Ms. McCarthy proceeded to explain that her son Evan’s autism symptoms appeared only after he received the vaccine for measles, mumps and rubella, known as MMR. That vaccine has long been associated with autism because of a flawed 1998 study. The prestigious journal Lancet eventually retracted the study, and a British government commission determined that its author,
Andrew Wakefield,
had acted “dishonestly and irresponsibly” in his research. Mr. Wakefield lost his license to practice medicine in the United Kingdom.

Yet the safety record of the MMR vaccine, along with details of Mr. Wakefield’s downfall, weren’t mentioned on the show. Instead, Ms. McCarthy made outrageous claims about the vaccine’s dangers while promoting equally ungrounded theories about “cures” for autism, including a diet she found on the internet.

In a brief moment of responsible journalism, Ms. Winfrey read a statement from the Centers for Disease Control and Prevention stating—accurately—that autism’s cause is unknown and that vaccines “protect and save lives.” This brief statement carried none of the emotional punch provided by the testimony of a struggling mom.

Despite employing dozens of producers and support staff, Ms. Winfrey failed to challenge Ms. McCarthy’s data or inform her viewers about the substantial body of scientific studies showing vaccines to be safe. Ms. Winfrey also failed to mention that major medical organizations such as the American Academy of Pediatrics and the American Medical Association affirm the safety of vaccines. Instead, the famous tastemaker put her trust in the famous actress, who, when asked about her own expertise, answered, “My science is [my son] Evan. . . . That’s my science.”

In Ms. Winfrey’s world of personal truths, this approach makes sense. Ms. McCarthy’s “truth” defied truths showing the opposite. She believed her son had been harmed by a vaccine. Therefore all vaccines are bad. Her “truth” didn’t have to make room for facts, such as a steady decrease in world-wide mortality rates because of widely available vaccines for diseases that once killed millions of people.

Ms. McCarthy benefited greatly from being a regular guest on “The Oprah Winfrey Show.” She used her association as a springboard to other programs—“The Doctors,” “The
Larry King
Show,” “Ellen,” “The Rosie Show” and others. Ms. Winfrey’s blessing also helped Ms. McCarthy land a season-long spot on “The View,” where she continued to promote her antivaccine message. The support of her beloved benefactress may have allowed Ms. McCarthy to convince thousands of parents to forgo vaccinating their children, which could be to blame for the resurgence of measles and other infectious diseases in the U.S.

While many Democrats seem thrilled that Ms. Winfrey could run for president, her vague and shifting sense of the truth is the very thing they often claim to despise about Republicans. The left was quick to criticize President
George W. Bush’s
“truthiness” and decries Mr. Trump’s use of “alternative facts.” But the antivaccine hysteria Ms. Winfrey helped incubate was more dangerous than mere “fake news.” It actually put people’s lives at risk.

Ms. Gunlock is a senior fellow at the Independent Women’s Forum and leads the organization’s Culture of Alarmism Project.